The present invention relates to the field of hydraulic control systems for the swing drives of cranes, backhoes, power shovels, and related apparatus.
For example, on a loader backhoe, there are a number of factors that reduce the performance of the swing system, including but not limited to air in the oil, inconsistent loads on the bucket, viscosity of the oil (temperature), and valve performance. These factors lead to control and performance issues such as backhoe oscillation, inconsistent stop control, and drift. Typically, swing control is accomplished by using an open circuit pump and a dedicated valve or sets of valves that are interposed between the pump and the hydraulic motors or hydraulic cylinders of the swing mechanism. Heretofore, such systems have proven to be complex in design and therefore expensive to manufacture. Thus, there is a need for swing control system that overcomes these deficiencies.
Thus, a primary objective of the present invention is the provision of an improved swing control system.
A further objective of this invention is the provision of a swing control system that utilizes a closed circuit pump to directly control hydraulic cylinders for swing control, thereby eliminating the need for complex and costly intervening swing control valving.
A further objective of the present invention is to provide a simple, inexpensive, and improved swing control system for a loader backhoe or the like.
A further objective of the present invention is a provision of a swing control system that is accurate, relatively insensitive to leakage, and reliable in use.
These and other objectives will be apparent from the drawings as well as from the description and claims that follow.
The present invention relates to a control system for the swinging of booms on backhoes, cranes, or similar material handling apparatus. This invention provides more direct control of the hydraulic swing cylinders and eliminates the need for additional complex valving and circuitry.
The control system of this invention is adapted for a material handling apparatus that includes a frame and a boom movably (usually pivotally or swingably) attached to the frame. A pair of double acting hydraulic cylinders on the frame connect in an opposing or inversely operating manner to the boom for swinging the boom with respect to the frame. The cylinders are hydraulically connected such that when fluid is supplied to one of the cylinders to extend its piston rod, that same fluid retracts the piston rod in the other cylinder, or vice-versa, to swing the boom with respect to the frame. The cylinders are directly controlled by a variable displacement hydraulic pump arranged in a closed circuit with the cylinders. The pump has a servo control associated therewith that is connected to a displacement varying means (such as a swashplate) disposed at least partially inside the pump, which establishes both the volume and direction of the flow of hydraulic fluid in the closed circuit. No separate swing control valve is required. The servo control on the pump is the sole means of controlling the cylinders.